Kermadec petrel

Pterodroma neglecta (Schlegel, 1863)

Geographical variation: Two subspecies are recognised: P. n.neglecta, which breeds widely across the south-west Pacific including on the Kermadec Islands (New Zealand), and P. n. juana, which breeds on the Juan Fernandez Islands and San Ambrosio Island (Chile) in the eastern Pacific.

The Kermadec petrel is a medium-sized gadfly petrel with highly variable dark, pale or intermediate plumage forms. Its variable plumage, along with its distinctive white wing flashes, bulky body and short, squared-off tail give it a skua-like appearance. The Kermadec petrel and similar Herald petrel are thought to mimic foraging skuas, and to use their resemblance of skuas to parasitise other seabirds for their food with more success than they would have otherwise.

The petrel takes its name from the Kermadec Islands, 1000 km north-east of the North Island of New Zealand. The islands were named in 1793 for Jean-Michel Huon du Kermadec, captain of the French naval ship, Esperance, whose crew were the first Europeans to sight the islands. In addition to its variable plumage, the Kermadec petrel is also unusual in having highly variable breeding times within the same island group. Very large numbers formerly bred during spring-summer (egg-laying in October-February) on Raoul Island, the largest of the Kermadec Islands. This population was extirpated by feral cats and rats between 1920 and 1967. In contrast, on the rat-free Meyer Islets, 2 km off Raoul Island, nests, eggs and chicks are reportedly present in varying numbers all year with a peak of egg-laying during February-March.

Identification

The Kermadec petrel has a bulky body, long pointed wings, and short, squared-off tail. Its highly variable plumage morphs range from birds with pale heads and underparts to birds that are completely dark. Many intermediate birds have a mid-brown head and upper breast, and white throat and remaining underparts. Birds in the South Pacific are polymorphic while birds at Indian and Atlantic Ocean breeding colonies are reported to be predominantly or exclusively dark. Some birds have pink legs and some have black legs; all have a black stubby bill. All birds have the same predominantly dark grey-brown wings, with white flashes near the end of the underwings and whitish primary shafts visible on the upperwings. Its flight is purposeful and direct, wheeling and banking in long glides interspersed with deep, gull-like wingbeats. They are generally solitary and silent at sea. The sexes are similar with no seasonal variations. Juveniles resemble adults.

Voice: Kermadec petrels are noisy at colonies, where calls include an explosive yuk-ker-a-oooo-wuk.

Similar species: the highly variable plumage morphs of the Kermadec petrel can make identification at sea challenging. Other seabirds with white flashes at the base of the primaries include: the very similar Herald petrel (not recorded from New Zealand) also with highly variable plumage morphs, never with a pale head, and does not have pale primary shafts on the upperwing; the providence petrel is greyer than dark morph Kermadec petrels, with a pale face and brownish head giving it a more hooded appearance. The three Stercorarius skuas have more direct, powerful, falcon-like flight with regular deep wingbeats and little use of soaring or banking (and often have elongated central tail feathers).

Distribution and habitat

Kermadec petrels breed colonially in the South Pacific at the Kermadec Islands, plus Balls Pyramid (Lord Howe), Phillip Island (Norfolk Island), Pitcairn, Austral, Tuamotu, Easter, Juan Fernandez and San Ambrosio Islands, possibly also Rarotonga; in the South Atlantic on Ilha da Trindade; and in the southern Indian Ocean on Round Island. They breed on all the Kermadec Islands apart from Curtis and L’Esperance Rock, with the largest population on the islets north-east of Raoul Island. They formerly bred in enormous numbers on Raoul Island, where a few birds may be recolonising following predator eradication.

Kermadec petrels nest on the ground under vegetation or in rock crevices. They range at sea across the subtropical South Pacific, the southern Indian Ocean, and both the southern and northern Atlantic Ocean. During breeding, birds occur at sea in the vicinity of breeding islands, occasionally south to the subtropical convergence at 44°S east of New Zealand but mainly between 20°S and 35°S. They are rarely seen off the New Zealand mainland. After breeding, some birds migrate north into the central North Pacific to 42°N towards Japan and the Aleutian Islands. New Zealand records away from the Kermadec Islands include one regularly at Cuvier Island (1973-1981) and single birds at sea off the Chatham Islands (March 1975), and off Kaikoura (January 1999). Seven beach-wrecked birds have been recorded from North Island beaches, mostly from Muriwai, with the southernmost in Hawke Bay. Several additional sightings off North Cape have yet to be submitted to the OSNZ Records Appraisal Committee for verification.

Population

The estimated global population of Kermadec petrels is 150,000-200,000 birds.

Threats and conservation

Cats and rats extirpated the formerly enormous population of Kermadec petrels on Raoul Island. Feral goats were eradicated from Raoul and Macauley islands in 1984 and 1970, respectively. Pacific rats were eradicated from Macauley in 2006 and feral cats and rats from Raoul Island 2002-2006. Since 2009 recordings of seabird calls have been played on automated broadcast equipment on Raoul Island in an attempt to attract Kermadec petrels (with no evidence as yet that this has worked).

Breeding

The Kermadec petrel is an annual colonial breeder with a variable breeding season at the Kermadec Islands. Very large numbers formerly bred mainly spring-summer on Raoul Island (egg-laying October-February). In contrast, on the Meyer Islets 2 km off Raoul island, nests, eggs and chicks are reportedly present in varying numbers all year, with a peak of egg-laying during February-March. The few birds on Macauley Island also breed in winter. Most New Zealand information is from the Meyer Islets. Kermadec petrels are monogamous with shared incubation and chick-care. After establishing a nest site on the ground surface, birds leave for 2-3 weeks to feed at sea before females return to lay. The single large (64 x 47 mm) white egg is mainly laid between August and March. Incubation takes 50-52 days, and chick-rearing 110-130 days. The chick is left alone by parents 10-14 days before it fledges.

Behaviour and ecology

Kermadec petrels are pelagic, rarely approaching land except to breed. At sea, they are thought to mimic foraging skuas and to use their resemblance of skuas to parasitise other seabirds. When attacking other seabirds in an attempt to take their food it mainly adopts a skua-like, fast and low horizontal flight.

Food

The diet of Kermadec petrels includes squid, fish and crustaceans, taken by surface-seizing, dipping and piracy.

Identification

A medium-sized gadfly petrel with a bulky body, long pointed wings, short squared-off tail, a black stubby bill and highly variable plumage morphs including that range from birds with pale heads and underparts, to completely dark birds and intermediate plumage birds. All have the same dark grey-brown wings with white flashes near the end of wings.